1. Technical Field
This invention relates to a capacitive pressure sensing semiconductor device that detects pressure applied from the external as change in capacitance.
2. Description of the Related Art
As one example of a position input device used as an input device for a personal computer and so forth, a device is known that consists of a position indicator having a pen-like shape, for example, and including a writing pressure detector, and a position detecting device having an input surface on which pointing operation and input of characters, figures, etc. are performed with the position indicator.
As the writing pressure detector of the position indicator, a capacitance-variable capacitor, for example, like that described in Patent Document 1 (Japanese Patent Laid-open No. Hei 4-96212) is used. The capacitance-variable capacitor described in Patent Document 1 has, as mechanical structural parts, a first electrode attached to one surface of a dielectric and a second electrode that is disposed on the other surface side of the dielectric opposed to said one surface and that has flexibility. The capacitance-variable capacitor further includes spacer means that separates the second electrode from said other surface of the dielectric by a slight gap except for a partial area, and still further includes a part that applies relative pressure or displacement force between the second electrode and the dielectric. When a writing pressure is applied to the position indicator having a pen shape, the flexible second electrode is displaced, which changes the capacitance.
Therefore, the capacitance-variable capacitor of the position indicator in Patent Document 1 has a large number of parts and these parts are mechanical parts. Thus, structure of the position indicator is rather complicated.
On the other hand, capacitive pressure sensors fabricated by a semiconductor microfabrication technique typified by a micro electro mechanical system (MEMS), for example, have been proposed as disclosed in Patent Document 2 (Japanese Patent Laid-open No. Hei 11-284204), Patent Document 3 (Japanese Patent Laid-open No. 2001-83030), Patent Document 4 (Japanese Patent Laid-open No. 2004-309282), and Patent Document 5 (U.S. Published Application No. 2002/0194919), for example.
The pressure sensors disclosed in Patent Document 2 to Patent Document 5 have a semiconductor structure including a first electrode and a second electrode disposed opposed to the first electrode at a predetermined distance. The distance between the first electrode and the second electrode changes depending on the pressure applied to the first electrode. Thereby, the capacitance formed between the first electrode and the second electrode changes. Thus, the pressure can be detected as a change in the capacitance.